1. Field
The present invention relates to pneumatic control systems for pneumatically powered hand-held tools. More particularly, the invention relates to proportionally controlled systems that allow for a distinct source of pressurized air to power the tool and to control the tool.
2. Description of the Related Art
Hand-held pneumatic power tools have been used for many years to increase the range of hand work in fields including hand engraving, jewelry stone setting, wood carving, and other similar tasks. Typically, these tools are designed to provide a variable range of power so that a user can produce desired results across a broad range of applications. To provide the user with variable power control, such pneumatic tools often have a control mechanism, such as a mechanical valve, either on the tool itself or within a separate control device, such as a foot control, to vary the air flow and/or pressure to or through the tool. Such valves often include a spring-loaded plunger that variably opens and closes an opening to increase or decrease the flow of pressurized fluid to the tool. Tools having mechanical valves have many disadvantages, however.
First, although mechanical valves are inexpensive, problems reported by users include inconsistent or excessive operating force and lack of repeatability. As can be appreciated, it is desirable that the tool provides the same amount of pressure based on the same actuation of the valve by the user. However, this is often not the case with prior art tools. Moreover, the tools are often not able to be used at low operating forces, which are preferred for delicate engraving, chiseling, or carving.
A second problem of prior art tools that use mechanical valves is that the tools do not provide the necessary control. For the delicate hand-working operations these tools are used for, it is necessary for the user to have complete control over the tool. Many prior art tools, however, exhibit mechanical friction and “stick/slip” within the tool. This prevents consistency during use and results in unexpected consequences when the tool sticks or slips during use. Moreover, the mechanical valves often have only a few levels of power output that can be selected by the user. This does not provide the desired control because it does not allow for the precision that accompanies selective power output over a range of values.
A third problem of prior art tools having mechanical valves is that the valves are not amenable to the high-stress environments that the tools are used in. For example, because the tools are used for engraving, chiseling, or carving, dust and debris is often pervasive, and such dust and debris irritates, wears, and hinders the performance of mechanical valves. Moreover, the mechanical parts of the valves become worn over time and must be replaced. Therefore, there is a need for a mechanism for controlling the tools that does not rely on a mechanical valve with multiple moving parts.
A fourth problem of prior art tools having mechanical valves is that the plunger of the valve exhibits appreciable mechanical travel. This directly affects the response time of the tool and/or the user's ability to precisely control the tool. For delicate operations, it is undesirable to have a slow response time.
A fifth problem of prior art tools is the lack of work flexibility due to the fixed configuration of the valve. Because a valve on a tool cannot be readily moved to another location or have its operating characteristics easily changed, tools having mechanical valves are not conducive to being used or held in a variety of ways. For example, for a hand-held tool, the valve is in one position, and thus, in order for the user to actuate the valve to vary the power, the user has only one option of holding the tool, namely the way in which the valve can be actuated. However, there are a variety of ways to hold and power a hand-held tool, such as with use of various fingers, the thumb, and the palm. Therefore, a hand-held tool that can be powered in a plurality of ways dependent on the user's preference is desirable.
Finally, depending on the physical attributes of the user, the user's preferred work configuration, such as sitting or standing, the specific task being performed, the size and shape of the article being worked on, and other factors, the optimum arrangement for the tool, including the preferred type of tool (e.g., hand-held tool or foot-controlled tool), may differ widely. Therefore, it is desirable to have several types of tools, including hand-held tools and foot-controlled tools, that can all be controlled in the same manner.
Accordingly, there is a need for an improved power tool that overcomes the limitations of the prior art. More particularly, there is a need for a new control system operable to variably control the power tool and to provide a mechanism that allows for more precision control and finesse of the power tool.